This invention relates to a filter system, and is particularly concerned with a multiple unit assembly of filter elements especially designed to remove particulate aerosol and vapor contaminants from air entering the aircraft before delivery of the air to the crew or equipment.
Filter devices have been used by the armed forces for protection of the crews of vehicles such as tanks, trucks and the like. However, the devices used on these ground vehicles are bulky, heavy and are not capable of withstanding the environment of high temperatures, high pressures and humidities supplied by aircraft environmental control systems and the physical location in the vehicle. Further, the prior art does not appear to disclose an efficient filter device for removing a combination of particulate, aerosol and vapor contamination from air, especially in the nature of chemical, biological and/or nuclear contaminants.
U.S. Pat. No. 3,922,152 describes a series type multiple stage filter and a parallel type multiple stage filter wherein each stage of the filter includes a tubular coil, a porous filtering media disposed in layers and for filtering gases, a cleaning liquid to a level above the porous filtering media through which the gases are passed for treatment. Such filter is useful in motor vehicle exhaust systems, for industrial applications, e.g. for filtering stack gasses, and for water purification. The filter is cleaned without removing it from its environment, for example when in the exhaust line of a motor vehicle. This filter device is not adapted to the removal of aerosols or particles.
U.S. Pat. No. 3,906,798, discloses a protector means for preventing moisture and oxygen present in a source of air from entering into a sealed housing and affecting the operation of an instrument located in the housing, comprising a filtering material having a first section which contains a zeolite and a second section containing silica gel particles, the zeolite absorbing oxygen, and the silica gel absorbing water vapor. This filter device is not adapted to remove vapors.
U.S. Pat. No. 4,256,474 discloses a two-piece twist apart filter housing adapted to be interposed in a conduit supplying or receiving air from a device, in particular the filter assembly employed therein includes a particulate filter, a coalescing filter and an odor filter. The use of a vapor filter element, however, is not disclosed.
U.S. Pat. No. 4,294,599 discloses an aerosol respirator cartridge employing the combination of a pre-filter comprised of glass fibres, in combination with final filtering components formed of resin impregnated wool felt. The patent does not disclose the use of a vapor filter element.
Further, in many prior art filter devices, particularly employing a plurality of filter elements, such filter elements must be individually removed from the filter unit for cleaning and thereafter replaced. Particularly where toxic substances such as toxic gases, biological contaminants and nuclear contaminants are present in the spent filter elements, this presents a substantial danger and hazard to personnel handling such filter elements during cleaning and replacement thereof.
It is an object of the present invention to provide a filter device or unit for removing contaminants from air, and comprising a plurality of filter elements to remove various types of contaminants from the air to provide clean air.
Another object is to provide a filter unit of the above type and designed primarily for use in aircraft, especially military aircraft.
A further object is the provision of a filter unit of the above type particularly designed to remove particulate, aerosol and vapor contamination from air before it is delivered to the crew or equipment in an aircraft.
A particular object is the provision of a filter system for removal of chemical and/or biological and/or nuclear contaminants from life support air.
A still further object is to provide an efficient multiple stage filter unit of the above type which is operable under varying pressures, temperatures and humidities, for removal of contaminants from air, especially contaminants of the above type, involving either straight through, i.e. series flow, or particularly parallel flow, employing multiple filter elements, and providing high capacity flow of air through the filter unit.